The Full Swing: What Happens With The Golfer & The Golf Club?
Why The Full Swing Matters
Designing golf clubs and also playing golf, in my opinion, requires a very good working knowledge of what happens to a golf club dynamically when swung with the intention of hitting a golf ball. There are many dynamic relationships that occur before, during and after impact that will take our knowledge to the next level of understanding.
The writing here is not theoretical, but rather a lifetime study of this process. I have done a tremendous amount of research in this area, starting with countless hours of machine and player testing and the recording of this data. I have been studying this topic for my entire life.
Background & Studies
In the 1970’s I was fortunate enough to work with Dr. Stanley Plagenhoff who was the head of the Kinesiology department at the University of Massachusetts and also was the author of the textbook used there.
Dr. Plagenhoff, his staff and myself traveled around the country and filmed numerous golfers from touring pros to every level of amateur using high-speed film cameras. The cameras captured golfers swings from every angle up to 5000 frames per second.
To better understand 5000 frames per second, imagine 125 feet of film going through the camera to only capture the top of the back swing to 3 feet after impact. The button was pushed and the camera motor went wwwhhhhiiiinnnngggg and it was all over.
Back at the University, graduate students analyzed every frame of film by blowing it up and inserting points at every human joint and every part of the moving golf club. This was done on every frame and the data was fed into a computer and analyzed.
This was a very time consuming and costly analysis but the results eliminated much of the myth that existed at the time and for some still today.
Since that time I have been involved in other studies and today, I have a modern high-speed camera in my studio that has the capability of 2000 frames per second and 1/40,000th of a second shutter speed.
Also, a number of televised golf events have been using high speed playback of touring pro swings and ball impacts. This is a great way to visually see what happens. I would caution viewers however that many times the personality explaining what you are seeing is often not accurate.
Breakdown of The Full Swing
The following explanations are not going to be in any particular order such as the takeaway, the back swing, the downswing etc. Rather, the discussion will work around the actual movements of the club and it’s physical properties.
These movements will mostly refer to the golf club, but there is also some discussion about the human interaction, as this is necessary for a better explanation. Keep in mind that all golfers are like snowflakes; no two are alike.
Couple this with the myriad of combinations of golf club parts and specifications and we have an infinite array of possible hitting results. So, keep in mind here that we are trying to explain in some detail, but in general terms, the dynamics of the golfer, the golf club and the ball.
There are three related but very separate rotations that occur with the clubhead during the swing.
The clubhead rotates about the shaft’s axis on the takeaway in a clockwise direction and rotates counterclockwise throughout the downswing. This rotation is partly a function of the moves that a golfer must use to get the club back and through to hit a golf ball.
More specifically, the golfer’s wrists roll open on the takeaway (pronation of the wrists) and rolls closed on the downswing (supination of the wrists). Remember that some golfers have very little natural rotation of the wrists in both directions and others much more. This can be a good discussion with a teaching professional if you are interested in this area.
The Down Swing
Rotation of the head is caused by a deflection of the shaft during the downswing. Basically, four dynamic changes to specifications occur to a swung golf club because of shaft flexing. The four dynamic changes are that the face angle closes, the loft angle increases, the lie angle flattens and the clubs length shortens. The flexing characteristic we are most interested in here is that the face angle closes since this is a form of rotation of the clubhead. The face closes because the golfer (due to releasing the wrists on the down swing) increases the head speed at an accelerating rate. The later the golfer releases the wrists the greater the clubhead acceleration. Because the head is traveling faster than at any other point along the shaft, the shaft bends forward (the head is out in front of the shaft) causing the face angle to close or the clubhead to slightly rotate.
The Back Swing
There can be rotation of the clubhead about its own center of gravity at impact, but only if the ball is impacted at any other spot than the clubheads horizontal center of gravity location. In other words, when the golf ball impacts the face on the horizontal center of gravity location, no measurable twisting of the clubhead occurs. Testing has shown that two additional points need to be made here.
First, regardless where the horizontal center of gravity is located, the golfer will find this spot because the club feels the most solid (less vibration) to impact the ball at this location. Of course, the individual golfers ability determines how often he hits this location or misses it.
Secondly, a golf club performs better and is easier to hit for the majority of golfers when the center of gravity is moved more toward the toe vs. more toward the heel. More specifically, it should be pointed out that testing has shown that a golfers ability to roll the face open on the takeaway and roll the face closed on the downswing are reduced somewhat with a horizontal center of gravity being moved farther away from the heel and more toward the toe.
This is good as it reduces one more variable for the golfer that can cause a problem with directional control. It also makes the clubhead more stable and thus more predictable in directional control.
Functions of A Golfer’s Swing
High speed photography shows that with any clubhead design, regardless of center of gravity location, that the natural tendency is for the club face to be slightly open coming into impact, square at impact and finally, starting to close after impact.
All of this is a function of the golfers’ swing and the shafts bending characteristics (already discussed) of that particular golf club in normal circumstances. Non-normal circumstances could be a less skilled player who may have the club face in numerous other positions, or any player with the wrong shaft flex (usually an extremely flexible shaft for a fast swing speed or too stiff a shaft for a slower swing speed).
Any rotation motion of the clubhead created by the golfer and/or the golf club throughout the swing cannot change the speed of the head coming into impact, at impact or after impact.
The speed that a golf club can be swung for a particular golfer is basically a function of the clubs length, overall weight, swing weight, head weight, weight distribution and its aerodynamic qualities.
The individual components and their properties determine the weight distribution of the golf club. Also, any shift in the center of gravity position toward the toe or heel will do nothing for increasing head speed.
Horizontal Face Bulge
The horizontal face bulge is very important on its own merit in hitting a golf ball in the desired direction. Determining the correct horizontal face bulge radius for any given driver or fairway wood (includes all wooden and metal woods) is quite simple.
Rearward Center of Gravity
The Rearward Center of Gravity is found and measured and is put into a formula which computes the bulge radius. This formula has been proven to be accurate through extensive player testing and robotic mechanical golfer testing by many different golf companies and individuals over a period of at least 70 years.
The Impact & The Gear Effect
When a golf ball is impacted in the center of the face (assuming also the center of gravity location), the horizontal bulge radius has virtually no effect on the directional control of the shot. On off-center hits, however, the proper horizontal bulge radius is a factor. On off-center hits, the horizontal bulge simply hits the ball more crooked and farther off-line.
A phenomenon called “the gear effect” creates a side spinning action to the golf ball. Sidespin on a golf ball either makes it curve right or left. Because wood type clubs have centers of gravity much farther rearward than do irons, wood type clubs impart a hooking sidespin on toe shots and a slicing sidespin on heel shots.
Hence, the horizontal bulge radius on the face hits the golf ball in the appropriate crooked or wrong direction to compensate for the hooking or slicing action on the golf ball so that it hopefully lands in the middle of the fairway.
If horizontal face bulge were put on most iron heads, on off-center hits the ball would be hit more crooked, but would not have adequate sidespin applied to it to correct its flight direction. This would not be good and is caused by the rearward center of gravity on most irons not being far enough rearward to create the “gear effect” that imparts the corrective sidespin.
The vertical face roll radius has no effect on the directional control of a golf ball. On shallow faced woods and metal woods, the vertical roll radius can be eliminated with no ill causes, although it will give the appearance of less loft than there really is.
The vertical gear effect is almost non-existent on these clubs. On drivers, it is more important to put the proper amount of vertical face roll because it will counteract the vertical “gear effect” that takes place (mostly more of a concern with the very big driver heads of today) and is basically explained in the same manner as horizontal bulge but the performance attributes are in a vertical or trajectory plane.
Vertical gear effect is not a factor on irons and putters. It can be concluded that while the horizontal face bulge radius can be a factor in directional control, the vertical face roll radius is not a factor in directional control, but can be a factor in trajectory control.
As a side note, it was once thought that the greater the bulge and roll radius (four way radius), the greater the clubheads penetration into the ball at impact resulting in greater distance. This has since been proven to be an insignificant factor with the specific common radius’s that are used on golf club faces.
The Head & The Shaft
It has already been mentioned earlier that four bending properties occur in the shaft when the club is swung. One of those was the head bowing down coming into impact thus causing the lie angle to flatten somewhat.
This is caused by the simple fact that the center of gravity of the head is not in-line with the axis of the shaft thereby causing centrifugal force to act through the offset center of gravity and bow the head downward.
It is true that the farther out the center of gravity from the shaft, the greater the bowing downward and this varies in progression from club to club within the set. Regarding irons, the number 2 iron will bow down more than say the number 9 iron. The weight of the head, the shaft flex, the club length and the speed it is swung are the key determining factors as to how much the lie angle flattens.
It is now apparent that many different shaft-bending attributes occur during the swing and to what extent they occur is due to the golfer and the golf clubs properties. The golf shaft is a very important factor in how easy or hard it is to hit a shot.
Think of the golf club as having two main performance parts, the clubhead and the shaft. Think of these parts as totally separate entities in hitting a golf ball. The golf shafts job is to simply bring the clubhead into impact with the ball with repeatability.
The bending attributes and all other shaft properties should perform exactly the same with every swing every time. Consistency is what we are looking for in a golf shaft design and one that works with our swing and the clubhead that is attached to it.
A tall order, but manageable with a knowledgeable club fitter or demo day hitting sessions before the purchase. Think of the clubhead as being a free wheeling object and completely on its own at impact. The shaft brought it there in a certain position, at a certain speed and now it hits the ball using its own mass and dimensional properties.
This is slightly simplistic because there are some shaft and head properties that overlap, but the important point to make here is to treat the shaft and the clubhead separately when determining all aspects of a golf club’s playability.
How The Full Swing Works
The golfer addresses the ball. During the takeaway, the clubhead lags behind the shaft (the shaft bows slightly backward). At the top of the back swing, the shaft bends in the opposite direction causing the clubhead to now go behind the shaft.
The Down Swing
The clubhead is accelerating on the downswing, during which the clubhead moves in front of the shaft (shaft bowing forward). Because the clubhead is in front of the shaft and the shaft is also bending downward, four characteristics change in the club compared to the address position.
First, the clubheads loft is increased. Second, the face angle closes. Third, the lie of the club flattens. Fourth, the length of the club actually shortens because the shaft is bent in basically two directions.
During impact, while the ball is flattening on the face, the shaft at some point becomes straight. The force of the impact does this. As the ball is just barely leaving the club face, the head once again goes behind the shaft due to the shaft bending backward (sort of a recoil effect).
As the clubhead continues into the follow through, the head comes in front of the shaft and goes behind the shaft at least three more times. When viewed in high-speed photography, it appears as if the shaft is a wiggling snake. Try to pick this up on the TV broadcasts using high speed cameras for analysis.
One last important point to make regarding the lie flattening during the swing due to shaft flexing. The actual flattening of the lie angle is greater than that which occurs due only to shaft flexing.
Here is what happens: the golfer at address has his hands in a certain position. During the swing, centrifugal force (pull) is exerted on the golfer due to the fact that a golf club has mass and is swung at high speed.
The pulling force acts on the body of the golfer mainly resulting in the golfers arms being more out stretched. When this happens, the golfers hand position is raised higher than it was at address.
Thus, the golfer unknowingly flattens the lie angle even more than just the shaft bowing downward effect. Since proper lie angle is a very important fitting variable regarding directional control, it is imperative that the lie angle be fitted properly to every golfer.